For example, to provide a sound in a space (acoustic space) having a substantial capacity such as an airport lobby, a speaker system designed to obtain constant directivity in a frequency range is in some cases used. A typical example of such a speaker system is a speaker system using a constant directivity horn (see e.g., non-patent document 1).
The speaker system using the constant directivity horn is frequently used in combination with a box speaker including a woofer unit attached to a cabinet. According to such a speaker system, in a frequency bandwidth provided by the constant directivity horn, directivity is controlled relatively stably. That is, constant directivity can be obtained in a relatively wide frequency range.
The speaker system using the constant directivity horn is typically coupled to the box speaker having the woofer unit by metal members. A combined system thus coupled has a great dimension, and has a complicated shape. For this reason, the combined system is not easily installed in the acoustic space.
There has been a need for a speaker system that is more compact than the constant directivity horn and is capable of obtaining constant directivity in a wider frequency range than that of the constant directivity horn.
A box-type speaker system including a woofer and a tweeter that are attached to a cabinet is in some cases used. This tweeter is a tweeter having a horn. Because such a speaker system is constructed in such a manner that the woofer and the tweeter are attached to the cabinet, it is easily installed in the acoustic space. Since the woofer and the cabinet are accommodated into the cabinet, preferable design is presented. However, since the horn of the tweeter is relatively small, the directivity cannot be controlled stably in a frequency bandwidth so wide as that of the constant directivity horn.    Non-Patent Document 1: Saeki Tamon “New edition speaker & enclosure encyclopedic information) (Japan) published by Seibundo Shinko Sya Co. Ltd. May 28, 1999, p 36 to 37